Weekly Hydro-meteorological Report, 18 July, 2013

Highlights

Monitoring and Prediction
Rainfall was quite heavy in June in the Southern half of Sri Lanka, and July is predicted to be lower although with wetter Southwestern regions in the next week. Compared to the rest of the island, the coastal belts of Gampaha to Galle is likely to receive heavier rainfall on coming two days (19th and 20th of July). Ongoing rainfall shall decrease gradually till 21st-23rd July & increase thereafter till 26th. However, relatively less rainfall event around 20th (trough) shall be expected for western coasts.

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Summary

Monitoring


Weekly Monitoring:Rainfall ranged between 5-40 mm during 9th-15th July 2013. Maximum rainfall observed for small region in Ratnapura district on 10th July. However, entire country experienced lower rainfall throughout the week compared to month of June 2013.


Monthly Monitoring:Southern half of the Sri Lanka received an above average rainfall during the month of June. The entire country received less than 15 mm of daily rainfall, with Ratnapura district receiving the highest rainfall during the month (14mm/day).

Predictions

7-day prediction:Southwestern and central hill regions shall receive 5-45 mm of rainfall and during 17th-23rd July 2013.

IMD WRF Model Forecast & IRI forecast:For 19thof July, IMD WRF model predicts less than 65 mm of rainfall for coastal regions of Galle district and it shall spread towards North-South directions of coasts & central hills in a reducing manner. For the 20th of July, coastal regions of Gampaha to Galle districts shall receive less than 35 mm of rainfall and it shall spread as previous day in a reducing manner. NOAA model predicts more rainfall for the Colombo to Galle districts during 15th-20th July compared to rest of the regions of Sri Lanka.

1 Month Prediction:Overall- Ongoing rainfall shall decrease gradually till 21st July & rainfall is likely to increase gradually thereafter. Significant rainfall events are not expected during next week period (19th-25th July). Western Slopes – The rainfall pattern persisting in the entire country shall be observed in this region, but rate of increase shall be higher than the entire country. Western Coast – The rainfall pattern persisting in the entire country shall be observed in this region. However, relatively less rainfall event is likely to be observe around 20th July. Eastern Slopes– The rainfall pattern persisting in the entire country shall be observed in this region. Eastern Coast – The rainfall pattern persisting in the entire country shall be observed in this region. But predicted average rainfall is higher compared to month of June. Northern region- The rainfall pattern persisting in the entire country shall be observed in this region. Southern Region- The rainfall pattern persisting in the entire country shall be observed in this region, but rate of decreasing shall vary with time. Rainfall is not predicted for 23rd-25th July.

Seasonal Prediction:As per IRI Multi Model Probability Forecast issued on June 2013; for July 2013 to September 2013, there is a 50-60% probability for temperature to be above normal in the country while the rainfall is to be climatological.

PACIFIC SEAS STATE July 5, 2013 :During Maythrough June observed ENSO conditions remained neutral. Most of the ENSO prediction models indicate a continuation of neutral ENSO into northern autumn. However few models, mainly but not exclusively statistical models, call for cooling towards borderline or weak La-Nina conditions during the coming northern summer season into the latter part of the 2013.

INDIAN OCEAN STATE :The sea surface temperature around Sri Lanka was anomalously cold during 7th-13th July 2013.
MJO STATE :MJO is entering phase 4 and is likely to enter phase 5 both of which not influences Sri Lanka rainfall.